The invention relates generally to adsorption methods.
Of particular interest to the invention are methods for the regeneration of contaminated adsorption agents.
The invention is especially concerned with the simultaneous thermal regeneration in fluidized state of contaminated particulate adsorption agents of different type and/or of different particle size, particularly adsorption agents which have been contaminated or loaded with waste water components.
Organic substances are removed from waste water by means of adsorption agents such as, for example, activated carbon, aluminum oxide and silica gel. Generally, waste water does not contain just one type of substance or just one class of substances. Rather, waste water contains complex mixtures of numerous substances. It has been found that, as a result of this, a single adsorption agent does not, as a rule, suffice for the complete adsorption of the organic substances from waste water.
On the other hand, it is possible to achieve a high degree of purification using more than one adsorption agent, e.g., by using adsorption agents such as aluminum oxide and activated carbon having polar and non-polar surfaces. A further alternative is to provide a plurality of purification stages arranged in series and to use the same adsorption agent, e.g., activated carbon, in each stage but with different particle sizes.
The thermal regeneration of contaminated adsorption agents has heretofore been carried out mainly in multistage ovens or rotating tubular ovens. Here, the adsorption agents continuously pass through the regenerating ovens. The regenerating ovens must not only be capable of treating the adsorption agents in a gentle fashion but must be designed so as to permit achievement of good heat and material transfer characteristics, as well as short dwell times.
A substantial improvement in the heat and material transfer characteristics achievable with multistage or rotating tubular ovens is made possible by the use of a fluidized bed reactor or oven.
Thus, it has become known to carry out the thermal regeneration of adsorption agents such as, for instance, activated carbon, in fluidized bed reactors having a plurality of individual fluidized beds arranged one above the other. Here, the fluidizing gases, as well as the vaporizing or gasifying agents, are conveyed in countercurrent to the adsorption agent to be regenerated. The adsorption agent continuously passes through the multistage fluidized bed reactor from top to bottom.
Although this multistage fluidized bed reactor possesses the advantages mentioned above, namely, improved heat and material transfer characteristics, it nevertheless simultaneously possesses several rather severe disadvantages. For instance, a relatively large reaction volume is required. Moreover, the individual stages must be connected with one another via the pipes through which the adsorption agent travels downwardly from a given stage to the next lower stage after having passed over an overflow weir (German Pat. No. 951,864).
Further known is an elongated, rectangular fluidized bed reactor provided with a foraminous wall through which a flow of gas takes place. Here, perpendicularly arranged baffles which form, or which are formed with, flow restrictions are positioned above the foraminous wall and extend transversely to the direction of travel of the solid particles being treated. The flow restrictions may be formed by openings provided in the perpendicularly arranged baffles. This construction is intended to achieve a uniform treatment of the individual solid particles during an operation such as, for example, the activation of carbonaceous substances with water vapor or activating gases at red heat temperatures (German Pat. No. 971,417).
However, constructions of this type have been found in practice not to be suitable for the regeneration of activated carbon since a portion of the activated carbon particles become overactivated thereby resulting in a loss of activated carbon.